The present invention relates to an optical disk apparatus and a recording/reproduction method therefor and, more particularly, to an optical disk apparatus for recording digital video data and other digital data such as audio data and system data on an optical disk (including magnetooptical disk), which is rotated at a constant angular velocity with a constant recording wave length, and a recording/reproduction method for the disk apparatus.
As a recording scheme for an optical disk, a CWL (Constant Wave Length)-CAV (Constant Angular Velocity) scheme is available, in which high-density recording can be performed, and a high-speed search can be made in the reproduction mode. In this scheme, while the rotational speed of an optical disk is kept constant, a recording operation is performed with a constant wave length.
As shown in FIG. 10, a conventional CWL-CAV optical disk apparatus rotates an optical disk 21, which has recordable upper and lower surfaces, at a constant angular velocity. This disk apparatus has optical heads 22 and 23 arranged on the upper and lower surface sides of the optical disk 21. The optical head 22 is moved from the outer periphery to the inner periphery of the optical disk 21, as indicated by an arrow A. The optical head 23 is simultaneously moved from the inner periphery to the outer periphery of the optical disk 21, as indicated by an arrow B. With this operation, data is recorded. In this case, the distances from the center of the optical disk 21 to the respective heads 22 and 23 are detected, and the peripheral velocity ratio between tracks on which the optical heads 22 and 23 are respectively located is obtained. Data distribution is then performed on the basis of the track peripheral velocity ratio such that the sum total of the bit rates of recording data supplied to the optical heads 22 and 23 is kept constant, thereby recording data with a constant wave length.
FIG. 11 shows the conventional optical disk apparatus. Referring to FIG. 11, the optical heads 22 and 23 are arranged at the upper and lower surfaces of the optical disk 21. The optical head 22 is scanned from the outer periphery to the inner periphery, while the optical head 23 is scanned from the inner periphery to the outer periphery. At the same time, pieces of head position information 31a and 31b are input to head position information detectors 41a, 41b, 61a, and 61b. The pieces of head position information 31a and 31b may be pieces of mechanical position information or track address information.
On the recording side, recording clock generators 42a and 42b generate bit clocks having frequencies corresponding to the pieces of head position information. In this case, when the optical head 22 or 23 is located at an outer peripheral position, the corresponding bit clock has a high frequency. When the optical head 22 or 23 is located at an inner peripheral position, the corresponding bit clock has a low frequency.
Subsequently, a recording signal processor 43 performs signal processing of an input signal 51 on the basis of the bit clocks from the recording clock generators 42a and 42b, thereby distributing video data to the optical heads 22 and 23 in accordance with the pieces of head position information. In this case as well, when the head 22 or 23 is located at an outer peripheral position, the corresponding distribution amount is set to be large. When the head 22 or 23 is located at an inner peripheral position, the corresponding distribution amount is set to be small.
On the reproduction side, reproduction clock generators 62a and 62b operate a phase-locked loop circuit (PLL) at a center frequency corresponding to the pieces of head position information 31a and 31b, thereby generating a bit clock synchronized with a reproduction signal.
After this operation, a reproduction signal processor 63 performs signal processing on the basis of the bit clocks from the reproduction clock generators 62a and 62b, and finally outputs an output signal 71.
A case wherein data is recorded on the optical disk 21 shown in FIG. 5, which has a diameter of 30 cm and recordable upper and lower surfaces, will be described below.
Assume that the outermost and innermost peripheries of a doughnut-like recording area of the optical disk 21 respectively have diameters of 28.9000 cm and 15.0568 cm. Also assume that the recording area of the optical disk 21 is divided into 103 equal areas in the radial direction, and data is recorded on each divided area at the same bit rate. The optical disk 21 is rotated at a constant angular velocity, and the peripheral velocity is proportional to the distance from the center of the optical disk 21. Therefore, the peripheral velocity on the outer periphery side is higher than that on the inner periphery side.
TABLE 1 ______________________________________ Upper- Lower Surface- Surface- Side Data Side Data Position of Up- Position of Distribu- Distribu- per-Surface- Lower-Surface- tion tion Side Optical Side Optical Amount Amount Step Head (cm) Head (cm) (SB) (SB) ______________________________________ 0 28.9000-28.7656 15.0568-15.1912 1730 914 1 28.7656-28.6312 15.1912-15.3256 1722 922 . . . . . . . . . . . . . . . 102 15.1912-15.0568 28.7656-28.9000 914 1730 ______________________________________
As the optical heads 22 and 23 at the upper and lower surfaces of the optical disk 21 are simultaneously moved from step 0 to step 102, the peripheral velocity ratio in areas where the optical heads 22 and 23 are respectively located gradually changes in 103 steps. In this case, data distribution is controlled such that the distribution amount of one of the optical heads 22 and 23 located on the outer periphery side is increased, while the data distribution amount of the other of the optical heads 22 and 23 located on the inner periphery side is decreased, in accordance with the peripheral velocity ratios. With this control, one-frame recording data can be recorded on one peripheral track on each of the upper and lower surfaces of the optical disk 21 with an almost constant recording wave length.
Assume that the amount of one-frame recording data is 2,644 sync blocks. In this case, a sync block (to be abbreviated as SB) is a data string consisting of a total of 192 bytes, i.e., a 2-byte sync signal, a 2-byte ID signal indicating an address, 172-byte data, and a 16-byte error correction code.
At the start of a recording operation, the upper-surface-side optical head 22 is located above the outermost track in contact with a circle having a diameter of 28.9000 cm, and the lower-surface-side optical head 23 is located above the innermost track in contact with a circle having a diameter of 15.0568 cm. At this time, the peripheral velocity ratio is 28.9000/15.0568.apprxeq.1730/914. Therefore, in step 0, 1,730 SBs of one-frame recording data consisting of 2,644 SBs are distributed to the upper-surface-side optical head 22, and the remaining 914 SBs are distributed to the lower-surface-side optical head 23. That is, the upper-surface-side optical head 22 writes 1,730 SBs per track within a track area ranging from a diameter of 28.9000 cm to a diameter of 28.765 cm. Meanwhile, the lower-surface-side optical head 23 writes 914 SBs per track within a track area having diameters ranging from 15.0568 cm to 15.1912 cm.
As the optical heads 22 and 23 are moved, 1.344 mm at a time, from step 0 to step 102, the data distribution amount of the upper-surface-side optical head 22 decreases stepwise by 8 SBs, and at the same time, the data distribution amount of the lower-surface-side optical head 23 increases stepwise by 8 SBs. At last step 102, the data distribution amounts of the upper- and lower-surface-side optical heads 22 and 23 are respectively set to be 1,730 SBs and 914 SBs. In this manner, data distribution is controlled in accordance with peripheral velocity ratios, thereby recording data with a constant recording wave length.
In the above conventional disk apparatus, in order to record data on an optical disk by the CWL-CAV scheme, the optical disk 21 having recordable upper and lower surfaces is used, and the optical heads 22 and 23 are respectively arranged on the upper and lower surface sides of the optical disk 21. Therefore, the optical disk 21 having recordable upper and lower surfaces and the two optical heads 22 and 23 are required. In addition, in the reproduction mode, since synchronization must be established between the optical heads 22 and 23 located on the upper and lower surface sides, problems are posed in terms of cost and mechanical precision.